Sound recording apparatus



1934. H. E. METCALF 1,969,143

SOUND RECORDING APPARATUS I n Filed July 14, 1951 OSC/LLATOR- MODULATOR E l i O c 0 W iiffil mwfi 5 .F z'g.2

INVENTOR.

HERBERT E. METCALF.

ATTORNEY Patented Aug. 7, 1934 UNITED STATES SOUND RECORDING APPARATUS Herbert E. Metcalf, Walnut Creek, Calif., assignor to Sound Laboratory Corporation,

Ltd, San

Francisco, Calif., a corporation of California Application July 14, 1931, Serial No. 550,681

Claims.

My invention relates-to apparatus for recording sounds on film, and particularly to apparatus for recording sound tracks on moving picture films by the variable density method.

Among the objects of my invention are: To provide an apparatus, having no moving parts, for impressing a sound track on a film; to provide an apparatus which is substantially indestructible, and which, under ordinary use, requires no replacement; to provide an apparatus wherein the elements of the sound track are of constant dimensions and accurately predetermined size; and to provide an apparatus capable of. making recordings of the best quality, and with a minimum of equipment;

Other objects of my invention will be apparent or will be. specifically pointed out in the description forming a part of this specification, but I do not limit myself to the embodiment of my invention herein described, as various forms may be adopted within the scope of the claims.

Referring to the drawing:

Figure 1 isa sectional view of the apparatus of my invention, the plane of section being through the recording head and the film, certain portions of the apparatus being shown schematically.

Figure .2 is a side elevation, and

Figure 3 a bottom elevation of the dielectrode used to accomplish the recording.

Considered broadly, the apparatus of my invention comprises a block or slab of insulating material, in one edge of which is formed a gap or recess of substantially the dimensions of a single. element of the sound track to be recorded.

1 Apair of. metallic electrodes are positioned on opposite sides of the slab, and a modulated electrical potential, preferably of a materially higher frequency than the highest pitch sound that is tobe recorded, is applied between these electrodes, the potential. .being sufliciently high to cause ionization within the recess. The diele ctrode is mounted in such a position that the film in its motion through the recorder passes across the gap or recess, the plane of the gap being preferably perpendicular to the direction of motion of the .film. For best results, a body'cf conductive material is mounted to contact the un sensitized side of the film, and the gap is held with its orifice closely adjacent to the emulsion side of the film. Under these conditions a latent image will be formed upon the film which varies in density with the intensity of ionization within the recess. This latent image is brought out by development as in the case of a latent image formed by light. The image issharplyand clearly marked, and substantially of the dimensions of the gap. The succession of such images formed as the film is uniformly passed across the gap, forms a sound track which differs from that formed optically only in the minuteness of its stem 2 and supported by a bracket 3, secured suitably to-the recording mechanism. Fixed to' the block 1 is a pair of semi-cylindrical blocks 5 and 6, and embedded within them a pair of opposed radially extending-metallic electrodes 7 and 8 re spectively, whose opposing faces are substantially coplanar with the diametral faces of the blocks 5 and 6. The word metallic is used as including those substances having the conductive properties of metals, such as carbon, antimony or like materials. v

The electrodes 7 connect with the pin or stem 2 through a vertical pin 10 whose upper end contacts with a horizontal pin 11 extending radially through a side of the upper block 1. The opening through which the pin 11 is inserted is preferably closed by a small plug of insulating material 12. The connections between the electrode 7 and the stem 2 are therefore entirely embedded in insulating material, and accidental contact or sparking therefrom is prevented. The electrode 8 extends to the outer surface of the block 6, and carries a connection extending upward to a contact screw 13 which secures it to the upper block 1.

The opposed faces of the electrodes '7 and 8 abut against an intervening block or slab 15 of solid (as differentiating from gaseous) insulating material, within the lower edge of which is formed a recess or gap 16. This plate of insulating material may be formed in a single block, as shown in Figures 2 and 3,the recess being cut by an extremely fine circular saw. However, owing tothe fact that the recess 16 is equal in length and width to a single element or cross-bar of the sound track to be recorded, it is preferable to build the slab of three laminae as shown in Figure 1. In practice I have formed these laminae from mica, quartz, and from the reconstructed cellulose which is marketed under the trade name Cellophane. Since the latter material may be obtained in thicknesses as low as five ten-thousandths of an inch, I have found it convenient to make the center lamina of cellophane, while the two outer laminae are formed of mica. The entire thickness of the slab is much exaggerated as shown in the drawing, being in practice of the order of five one-thousandths of an inch thick.

It is to be understood that it is merely a matter of convenience that the insulating materials used in the various parts of the apparatus differ. For the sake of convenience I have used separate blocks of bakelite for the parts 1, 5, 6, and 15, but if desired, the entire assembly can be formed of a single molded block with the recess 16 formed therein. As shown, the recess does not actually extend into the space between the two electrode faces, but this is optional.

The film 1'7 upon which the record is to be made is pulled across the gap by any .suitable mechanism, this being indicated in the drawing by the sprocket 18. The sensitized side of the film passes adjacent the recess 16. The unsensitize'd side of the film preferably contacts with a roller or other conducting body 20, which serves to position the film and also increases the effectiveness of the markingas will be discussed later.

Electrical currents representing sounds are delivered from a microphone 21 to an oscillatormodulator 22, which is designed to produce oscillations of a frequency higher than the highest pitched sound that it is desired to record, modu lated by the current from the microphone 21. These modulated high frequency currents are delivered to the primary winding 23 of a high frequency transformer, whose secondary winding 25 connects through-a terminal screw 26 with the stem 2 and electrode 7, and through contact 13 with the electrode 8. The secondary 25 is preferably provided with a grounded center tap 27. The conducting body 20 is. also preferably connected to ground.

When oscillating potentials of the order of 2,000 to 5,000 volts are impressed across the electrodes '7 and 8, the gas within the recess 16 becomes ionized, and a mark, substantially the size and shape of the recess, is impressed upon the film. As the film is moved by the sprocket 18, a continuous succession of these marks of varying density forms a sound track which may be reproduced in, the same manner as the usual sound track formed by light.

It will be seen that the gas ionization takes place entirely within and between the dielectric material 15 and that there is no conductance to the gas in the gap from the metallic electrodes,

and that the energy is released in the gap by the susceptivity of the dielectric barriers. Conductance is characterized by the fact that the passage of a given amount of current is no bar to further current at a given potential; while susceptance means that the passage of current at any one point is a very definite bar to further current at a given voltage. The elimination of conductance by forcing all energy to travel a dielectric path before being released in the gas, prevents arcing, hissing and unstable discharges, and causes the ionization to be even, smooth and quiet even when wide gaps are used.

A certain amount of luminosity is produced by the ionized gas within the gap 16. That this lightis not the primary cause of the marking of the film is indicated by its extremely low intensity, by the fact that the density of the marking-of the film is materially decreased by the substitutionof a non-metallic member in place of the body 20, and by the fact that reversing the film, so that its unsensitized side faces the film causes it to remain practically unmarked.

I am aware that Tykociner has produced a device for making sound tracks on films by means of a discharge across a microscopic gap. The phenomenon here described differs from that of Tykociner in several including sapphire, quartz,'and mica, have been utilized in the insulating plate 15 without effecting the marking of the film. It will be noted that these materials are all of high dielectric coefficient, and therefore have high susceptivity. Second, the device of my invention requires an appreciable space within the air gap or recess 16, whereas Tykociner specifies that his air gap is of molecular dimensions, i. e., that the surfaces between which the discharge takes place are in as close contact as it is physically possible to produce. Furthermore, Tykociners effect upon the film appears to ,beproducedby light, whereas the marking of the mm by my invention appears to occur due to the bombarding of the film by ions generated within the gap. These ions seem to produce a charge upon the surface of the film, which tends to check further bombardment by ions of the conductive body 20 increases the effective capacity of thefilm so that this inhibitionjof further bombardment practically ceases to exist.

I find that an exploring electrode inserted with in or adjacent the recess 16 accumulates a nega tive charge. For this reason I believe that the ions which escape from the recess and bombard the film are only those which move most rapidly, i. e., electrons. The evidence is as yet, however, insufiicient to support any theory'of the operation of my device, and numerousof its attributes are yet to be explained.

Experiment has shown thatithe apparatus here described marks positive films and negative films with approximately equal intensity, whereas the sensitivity of the two filmsvmentioned to light is in approximately the ratioof 1 to 15.

Owing to the extremely small dimensionsof the recess 16, and to the fact that the discharge therefrom which marks the film, whatever may be its nature, does' not. spread appreciably, I have been able to impress frequencies as high as 18,000 cycles per 'second'upon film traveling at the standard talking moving picture speed of 90 feet per minute, and I have also impressed frequencies as high as 5,200 upon 16 millimeter film traveling at a speed of 35.1eet per minute. These frequencies are greatly in excess of those that can successfully berecorded by apparatus now in commercial use.

I claim:

1. A recorder for impressing a sound track upon a photographic film or the like comprising a pair of opposed metallicelectrodes, a layer of solid dielectric material disposed between said electrodes in contact with and covering the opposing faces of each electrode and having a gap formed therein substantially parallel to the plane of said layer to provide a solid dielectric path between each of said electrodes and said gap, and means for applying an electrical potential to said electrodes to cause ionization within said gap.

2. A recorder for impressing a sound track upon a photographic film or the like comprising a pair of opposed metallic electrodes, means-for insulating said electrodes from-the film, a layer of solid dielectric material disposed between said electrodes in contact with and covering the oppoimportant particulars. First, the best insulating materials procurable,

of the same sign. The. use.

site faces of each electrode and having a gap formed therein substantially parallel to the plane of said layer to provide a solid dielectric path between each of said electrodes and said gap, and means for applying an electrical potential to said electrodes to cause ionization within said gap.

3. A recorder for impressing a sound track upon a photographic film or the like comprising a pair of opposed metallic electrodes, solid dielectric material in contact with and covering the opposed faces of said electrodes and disposed to provide an air gap opening toward said film, and means for applying an electrical potential to said electrodes to cause ionization within said gap.

4. A recorder for impressing a sound track upon a photographic film or the like comprising a block of insulating material, and a pair of metallic electrodes embedded within said material and having opposed faces spaced within said block, said block having a gap extending inwardly from its surface nearest said film in a plane between said electrode faces and substantially parallel thereto, whereby a solid dielectric path is provided between each of said electrodes and said gap.

5. A recorder for impressing a sound track upon a photographic filmor the like comprising a pair of metallic electrodes mounted in opposed relation with substantially parallel spaced faces, solid dielectric material positioned between said faces and having a gap formed therein substantially parallel to the plane of said faces to provide a solid dielectric path between each of said electrodes and said gap, and a conducting body spaced from said gap to permit the passage of said film between the gap and said conducting body, said conducting body being connected to the circuit at a point whose operating potential is intermediate toy that of the electrodes.

6. The combination with means for imparting uniform motion to a photographic film, of a sound recording head comprising a pair of electrodes mounted with opposed faces in planes transverse to the direction of motion of the film and on the emulsion side of said film, and dielectric material disposed between said faces, said dielectric material having a gap formed therein opening toward said film and in a plane substantially perpendicular thereto.

'7. The combination with means for imparting uniform motion to a photographic film, of a sound recording head comprising a pair of electrodes mounted with opposed faces in planes transverse to the direction of motion of the film and on the emulsion side of said film, dielectric material disposed between said faces, said dielectric material having a gap formed therein opening toward said film and in a plane substantially perpendicular thereto, and a conducting body spaced from said sound head to contact the unsensitized side of said film and maintain the emulsion side of the film a predetermined distance from the orifice of said gap.

8. The combination with means for imparting uniform motion to a photographic film, of a sound recording head comprising a pair of electrodes mounted with opposed faces in planes transverse to the direction of motion of the film and on the emulsion side of said film, dielectric material disposed between said faces, said dielectric material having a gap formed therein opening toward said film and in a plane substantially perpendicular thereto, a conducting body spaced from said sound head to contact the unsensitized side of said film and maintain the emulsion side of the film a predetermined distance from the orifice of said gap, means for applying a modulated potential to said electrodes, and means for maintaining said conducting body at a potential intermediate said electrodes. I

9. The combination with means for imparting uniform motion to a photographic film, of a sound recording head comprising a pair of electrodes mounted with opposed faces in planes transverse to the direction of motion of the film and on the emulsion side of said film, dielectric material disposed between said faces, said dielectric material having a gap formed therein opening toward said film and in a plane substantially perpendicular thereto, and means for applying a modulated electrical potential between said electrodes.

10. The method of impressing a sound track upon a photographic film or the like which comprises the step of passing said film across a semiconfined body of ionized gas while substantially preventing electrical conduction to said gas, and altering the degree of ionization of said gas in accordance with the sound impulses to be recorded.

11. The method of marking a photographic film with a body of solid dielectric material having a recess therein wherein is enclosed a gas, which includes the steps of applying a potential to opposite faces of said dielectric sufiicient to ionize the gas within said recess, and moving said film past said recess.

12. The method of marking a photographic film with a body of soliddielectric material having a recess therein wherein is enclosed a gas, which includes the steps of applying a potential to opposite faces of said dielectric sufiicient to ionize the gas within said recess, modulating said potential in accordance with a train of electrical impulses, and moving said film past said recess.

13. A recorder for impressing a sound track on a photographic film or the like which comprises a pair of conductive electrodes having opposed faces, an air gap between said faces, and a barrier of susceptive material having negligible conductivity between each of said faces and said air gap.

14. A recorder for impressing a sound track on a photographic film or the like which comprises a pair of conductive electrodes having opposed faces, an air gap between said faces, and a barrier of mica between each of said faces and said air gap.

15. A recorder for impressing a sound track on a photographic film or the like which comprises a pair of conductive electrodes having opposed faces, an air gap between said faces, and a barrier of corundum between each of said faces and said air gap.

HERBERT E. METCALF. 

